1. Field of the Invention
This invention generally relates to optimize an optical device's operation. More particularly, the present invention relates to obtain more reliable operation parameters during the initialization to better facilitate the optical device's operation. In particular, such operation parameters provide an enhanced calibration for correcting Radial Tracking Error during the optical device's normal operation.
2. Description of Related Art
Before starting obtaining data from any optical storage media, the optical drive will start initializing the analogue front-end of the chip (CD/DVD chip). This initialization obtains multiple operation parameters to perform and to calibrate focusing, radial tracking, turn table motor control, and data retrieval.
One of the calibrations performed is the adjustment of the Radial Tracking Error (RE), which amongst others is used to keep the reading spot on track during normal playback. The algorithm that performs the calibration measures an initial minimum value and an initial maximum value of the RE-signal during track crossings, and the algorithm further determines over a period of time an average minimum and an average maximum value. Based on these values, the amplitude and the offset of the RE-signal are calculated and calibrated.
As the algorithm for calculating RE adjustment requires tracks to be crossed, the Optical Pick-up Unit (OPU) must be in focus. Therefore, the focus controller is switched to ON, and the Turn Table Motor (TTM) is also turned on in order to rotate the optical storage/disc. During this initializing/averaging period, sufficient track crossings are necessary in order to obtain a reliable measurement; but this is not always the case. In a first scenario that when a disc has eccentricity, there would be track-crossing points where the reading spot has zero velocity relative to the tracks. Because of the zero velocity relative to the tracks, any averaged values at these points might not be reliable. In a second scenario that when a disc has no eccentricity, there may be only very few track crossings or even no track crossing per averaging period, which does not provide sufficient information and thus results in a very unreliable measurement of the average RE amplitude and offset. A poor RE-signal calibration results in a degraded playability performance.
Referring to FIG. 1 of the drawing, the left graph 1 of FIG. 1 shows a number of signals during start-up/initialization of a conventional optical drive. From top to bottom, the signals shown are the Focus Actuator (FA), the Radial Actuator (RA), the sum of four light receiving parts A, B, C and D detectors (HF), and the Radial Error (RE) signal. The part of the start-up sequence that is of interest in this invention is marked with “RE calibration”. During the period of the RE calibration, the focus controller is turned on, the disc rotates and in the HF, and the RE signal the track crossings are visible. However, the radial controller is not active.
The right graph 2 of FIG. 1 shows an enlarged view of a small section at the beginning of the RE calibration period in the left graph 1 in FIG. 1. The right graph 2 shows the turning points of the disc eccentricity where the relative velocity between the reading spot and the disc becomes slower and to zero, and then the velocity accelerates again in the opposite direction.
When these turning points are long enough, they can influence the reliability of the RE calibration. Furthermore, if these turning points occur between two tracks, the acquisition circuitry will not be able to detect any pits. The absence of pits detection will be interpreted the HF loss, which will trigger a HF recovery and force the RE calibration to be re-started subsequently. This chain reaction causes a significant prolonging in the initializing process and delays the optical device's normal operation.
The reliability of the RE calibration also decreases on discs with a very low eccentricity or almost no eccentricity. In the case of low or no eccentricity, the RE calibration procedure might even fail completely due to insufficient number of track crossing during the calibration period. Even if the poor RE calibration does not fail the playability of the optical drive, the operation parameters obtained from the insufficient track crossings will not be the optimum or correct values, and the optical drive's performance will deteriorate as a result of it.